Re: [PATCH v5 3/7] s390/percpu: Use new percpu code section for arch_this_cpu_add()
From: Alexander Gordeev
Date: Tue Jun 02 2026 - 07:42:19 EST
On Tue, May 26, 2026 at 07:56:58AM +0200, Heiko Carstens wrote:
> Convert arch_this_cpu_add() to make use of the new percpu code section
> infrastructure.
>
> With this the text size of the kernel image is reduced by ~76kb
> (defconfig). Also more than 5300 generated preempt_schedule_notrace()
> function calls within the kernel image (modules not counted) are removed.
>
> With:
>
> DEFINE_PER_CPU(long, foo);
> void bar(long a) { this_cpu_add(foo, a); }
>
> Old arch_this_cpu_add() looks like this:
>
> 00000000000000c0 <bar>:
> c0: c0 04 00 00 00 00 jgnop c0 <bar>
> c6: eb 01 03 a8 00 6a asi 936,1
> cc: c4 18 00 00 00 00 lgrl %r1,cc <bar+0xc>
> ce: R_390_GOTENT foo+0x2
> d2: e3 10 03 b8 00 08 ag %r1,952
> d8: eb 22 10 00 00 e8 laag %r2,%r2,0(%r1)
> de: eb ff 03 a8 00 6e alsi 936,-1
> e4: a7 a4 00 05 jhe ee <bar+0x2e>
> e8: c0 f4 00 00 00 00 jg e8 <bar+0x28>
> ea: R_390_PC32DBL __s390_indirect_jump_r14+0x2
> ee: c0 f4 00 00 00 00 jg ee <bar+0x2e>
> f0: R_390_PLT32DBL preempt_schedule_notrace+0x2
>
> New arch_this_cpu_add() looks like this:
>
> 00000000000000c0 <bar>:
> c0: c0 04 00 00 00 00 jgnop c0 <bar>
> c6: c4 38 00 00 00 00 lgrl %r3,c6 <bar+0x6>
> c8: R_390_GOTENT foo+0x2
> cc: b9 04 00 43 lgr %r4,%r3
> d0: eb 00 43 c0 00 52 mviy 960(%r0),4
> d6: e3 40 03 b8 00 08 ag %r4,952
> dc: eb 52 40 00 00 e8 laag %r5,%r2,0(%r4)
> e2: eb 00 03 c0 00 52 mviy 960,0
> e8: c0 f4 00 00 00 00 jg e8 <bar+0x28>
> ea: R_390_PC32DBL __s390_indirect_jump_r14+0x2
>
> Note that the conditional function call is removed.
>
> Signed-off-by: Heiko Carstens <hca@xxxxxxxxxxxxx>
> ---
> arch/s390/include/asm/percpu.h | 65 ++++++++++++++++++++++------------
> 1 file changed, 43 insertions(+), 22 deletions(-)
Acked-by: Alexander Gordeev <agordeev@xxxxxxxxxxxxx>